Risk of tuberculosis among air passengers estimated by interferon gamma release assay: survey of contact investigations, Japan, 2012 to 2015

Abstract

Although the World Health Organization recommends contact investigations around air travel-associated sputum smear-positive tuberculosis (TB) patients, evidence suggests that the information thus obtained may have overestimated the risk of TB infection because it involved some contacts born in countries with high TB burden who were likely to have been infected with TB in the past, or because tuberculin skin tests were used, which are less specific than the interferon gamma release assay (IGRA) particularly in areas where Bacillus Calmette-Guérin (BCG) vaccination coverage is high. We conducted a questionnaire survey on air travel-associated TB contact investigations in local health offices of Japan from 2012 to 2015, focusing on IGRA positivity. Among 651 air travel-associated TB contacts, average positivity was 3.8% (95% confidence interval (CI): 2.5–5.6) with a statistically significant increasing trend with older age (p < 0.0094). Positivity among 0–34 year-old contacts was 1.0% (95% CI: 0.12–3.5%), suggesting their risk of TB infection is as small as among Japanese young adults with low risk of TB infection (positivity: 0.85–0.90%). Limiting the contact investigation to fewer passengers (within two seats surrounding the index case, rather than two rows) seems reasonable in the case of aircraft with many seats per row.

A tuberculosis contact investigation involving a large number of contacts tested with interferon-gamma release assay at a nursing school: Kanagawa, Japan, 2012

“…3.5% [95% CI: 1.6–6.6%] in the 35–54 year age group). ( 8 ) Also, there was a statistically significant trend in the risk of TB infection among the staff members and students ordered by duration of close contact, implying a dose–response relationship seen in previous studies. ( 13 ) These findings suggest that this event was a TB outbreak that was propagated from the index patient to staff members and students.…”

“…During the investigation, almost the entire staff and student body were screened for TB infection by IGRA, which makes the results of the investigation more accurate than when TST is used in settings with high BCG coverage such as in Japan. ( 6 – 8 , 11 , 12 ) The staff who shared an office with the index patient were 17 times more likely to have LTBI than the intermediate contacts consisting of third-year students. Although the staff members were older than the students, IGRA positivity among middle-aged Japanese men and women is not normally as high as 19% (e.g.…”

“…TB contact investigations in Japan rely on IGRA ( 1 , 6 , 8 ) rather than TST to screen latent TB infection (LTBI). IGRA is more specific and avoids interference caused by Bacillus Calmette–Guérin (BCG) vaccination, ( 9 ) which an estimated 90–95% of the population receives.…”

The use of host factors in microbial forensics

“…These are readily distinguishable by history and clinical information. Similarly, individuals infected with active tuberculosis will likely have a positive skin test (Mantoux) or a positive interferon-gamma release assay (Dewan et al, 2006;Ota and Kato, 2017), whereas the uninfected healthy person will be negative. In certain instances, a sick person with a cell-mediated immune deficiency will be anergic, that is, he/she will be negative to multiple skin tests including common antigens such as Candida.…”

Ending tuberculosis in risk groups in Europe: challenges from travel and population movement

“…For example, the yield of active TB among migrants from high- to low-burden countries ranged from 7 to 10,186 per 100,000 people screened, depending on various factors including the TB prevalence in the country of origin [ 2 ]. In this World TB Day issue of Eurosurveillance , four papers describe the risks of TB infection and disease in two potentially high-risk groups: migrants [ 4 , 5 ] and airline passengers [ 6 , 7 ].…”